I recently tried to boot my Kubuntu 12.04 LTS on my Sandy Bridge Laptop with i915.i915_enable_rc6=1, i915.i915_enable_fbc=1 and i915.lvds_downclock=1. I had some issues with 3D performance where somebody suggested using those options.

Since the resolution was not set correctly, I just tried it again with i915.i915_enable_rc6=1, i915.i915_enable_fbc=1. Then I rebooted and did not set any options manually, so everything should be reset. But since then, some KWin effects, especially wobbly windows does not work any more.

I also tried to boot some older kernel, but that did not have any effect.